Ultrasonic diagnosis apparatuses have been widely used for observation and diagnosis of blood flows in living bodies. An ultrasonic diagnosis apparatus generates and displays blood flow information from reflected waves of ultrasound by a Doppler method based on the Doppler effect. The blood flow information generated and displayed by the ultrasonic diagnosis apparatus includes a color Doppler image, a Doppler spectrum, etc.
A color Doppler image is an ultrasonic image captured by a Color Flow Mapping (CFM) method. In the CFM method, transmission/reception of ultrasound is performed on a plurality of scan lines in a region (two-dimensional region or three-dimensional region) including a site to be observed or diagnosed. In the CFM method, a moving target indicator (MTI) filter is used to remove frequency components derived from the motion of tissues from echo data and extract data of blood flow components, and the data of blood flow components is subjected to frequency analysis by autocorrelation, whereby the velocity of blood flow, the distribution of blood flow, and the power of blood flow are calculated. The color Doppler image is an ultrasonic image that two-dimensionally displays the distribution of those calculation results in color. In the CFM method, a method called alternate scan for improving the ability of detecting blood flows at low flow rates and a method that allows capture of color Doppler images at high frame rates are known.
On the other hand, a Doppler spectrum is data collected by a Continuous Wave (CW) Doppler method or a Pulsed Wave (PW) Doppler method. In the CWD method or the PWD method, transmission/reception of ultrasound is performed in time sequence on a single scan line including a site to be observed or diagnosed. In the CWD method, a high pass filter (HPF) having similar filter characteristics as the MTI filter is used to extract data of blood flow components on the scan line from time-sequential echo data. In the PWD method, data of blood flow components in a sample volume (for example, one point) on a scan line is extracted from the time-sequential echo data in the sample volume (also called a range gate) set on the single scan line.
In the CWD method and the PWD method, the blood flow information (the velocity of blood flow, the distribution of blood flow, and the power of blood flow) is calculated by performing frequency analysis on such data of blood flow components by a fast fourier transform (FFT) method. In the CWD method, the average blood flow information on a scan line is output, whereas in the PW Doppler method, the blood flow information in a sample volume on a scan line is output. The Doppler spectrum is an image of a spectrum obtained by plotting information of the calculation results in time sequence. The display of a Doppler spectrum is also called FFT display.
In the FFT display with a single scan line, the blood flow behavior in a one-dimensional region of interest can be observed precisely with good time resolution. However, the blood flow behavior in a two-dimensional or three-dimensional region of interest cannot be observed with the FFT display.